Sinn Féin took a historic step towards restoring devolution yesterday when the party's executive agreed to call a special conference to vote on whether to support the Police Service of Northern Ireland.

Following intensive negotiations with the government, party leaders gathered in Dublin to discuss proposals tabled by Sinn Féin president Gerry Adams. The full conference, or ard fheis, will be in January.

In a statement after the six-hour meeting, the executive said the motion to be put to the conference would "actively encourage everyone in the community to cooperate fully with the police services in tackling crime in all areas and actively supporting all the criminal justice institutions". It would also seek to exclude MI5 from any role in "civil policing".

Speaking later, Mr Adams added: "We stayed out of policing structures until now, in order to bring about maximum change. If the ard fheis accepts this motion, it will be about us going into a new political dispensation in order to continue to bring about maximum change and to ensure that the police never again do to our people what they did before."

The refusal to endorse the PSNI is one of the final obstacles to reconvening a Stormont assembly with full powers.

Sinn Féin has demanded that powers governing policing be devolved to the assembly, as they are in Scotland. The Democratic Unionist party opposes the idea of a republican politician - probably a former IRA member - having control of security policy in the immediate future.

Northern Ireland secretary Peter Hain said: "This move... compares in scale to the IRA giving up its war on July 24 last year, followed by the decommissioning of its weapons. Full cooperation by republicans with the police over issues like rape and burglaries is vital if Northern Ireland is to go into the new year with a spring of confidence to achieve devolution by the D-day of March 26."

One possible compromise involves neither Sinn Féin nor the DUP being given the job of security minister. It would be taken by an Ulster Unionist or Social Democratic and Labour party assembly member.